I am new to gardening and I have started to grow my own vegetables at home. I have used only compost - and now that I am reading more about gardening, I am not sure if what I did was right. So do I have to add soil to compost to grow my vegetables?
It depends. In the UK people used to buy bags of compost and plant tomatoes in them instead of replacing the diseases soil of their greenhouses. The bags did need careful watering, sometimes twice daily.
Commercial compost might contain all sorts of nasty things which you may not wish to use. So, using your own compost is probably best. And usually there is some soil used as an activator in your own compost.
There are some plants that seem to thrive in growing in a compost heap eg. pumpkin or squash
The proponents of straw bale gardening are essentially growing in compost as it's being made.
And I have an avocado tree that is over one storey high growing out of one of my now unused compost bins.
So, it's doable with the right compost, and the right plants. And you'll likely need some potash if you're growing flowering vegetables.
I am unable to tell if you are growing in pots or out in your yard. But the answer in both places is no. Compost should be mixed with soil out in the garden. Compost should never be added to pots in doors. On the patio, compost in pots is fine by applying a few inches to the top of the soil (potting soil) but only for established longer term plants that are outside that need their soil 'refreshed'.
Soil in pots should always be sterilized potting soil. No additives. Pots always always with a drain hole, should be cleaned with bleach and dried then filled 1/3 with potting soil, plant a start, fruff up the roots a bit, firm the soil as you fill in layers. Firm gently. Fill and firm up to 1" beneath the rim. The crown of your plant should be beneath the soil and any wood trunks/stems have to be above ground.
You most certainly should do this with your plants, replant in sterilized potting soil. If you peruse our questions and answers you will find that most problems with growing plants in pots, containers is because sterilized potting soil was not used.
If you are newish to growing plants, just use Osmocote Extended Release Fertilizer 14-14-14. A balanced fertilizer you only need to use once during the growing season for annual vegetables. This fertilizer is almost bullet proof if you follow the directions. I only do half the number of applications whether my garden out of doors or my pots.
Later on, you'll want to get into the science of chemistry and botany and try some different 'organic' fertilizers. Don't mess with adding anything else to your soil. Organic material has to be decomposed. Never ever fresh.
Compost should never be used in place of soil, pots should only have sterilized potting soil, compost should never be considered fertilizer either. There are minute traces of chemicals plants need but never a balanced formula. You have to know the chemistry of your soil before adding any extra chemistry (fertilizer). Too much of one chemical while it may not kill your plant will almost certainly cause deficiencies and excesses that will weaken your plant and cause secondary problems such as insect damage and disease.
Just a little too much chemistry (some people say 'nutrients' plants make their own food)! will kill plants, easily, quickly and completely. NPK, get to know this term. Nitrogen, Phosphorus, Potassium (potash). You'll find the formula in 3 numbers; such as 14-14-14 that I mentioned. This means in the package, there will be 14 percent Nitrogen, 14 percent Phosphorus, 14 percent Potassium. Nice safe formula.
If you want vegetables that need to flower to produce seed/fruit such as tomatoes, eggplant you need to make sure that the nitrogen percentage is never higher than the P and the K. If 14-14-14 were 15-14-14 you would get more vegetative growth (can't eat tomato plant leaves) than reproductive (flowers and fruit). This could cut the production of your tomato plant by half and more. Compost? There might be nitrogen available in your compost. Add compost and you could easily boost the nitrogen to your tomato high enough to inhibit flowering. This is important.
If you used just potash, potassium...compost with a little or unknown Nitrogen content...you still do not know that you have a balanced fertilizer component in that soil. What about the phosphorus? I never buy potting soil with added fertilizer (or even water holding gels or sponges). I like knowing what it is that I have added. Otherwise you have to wait until the plant shows signs of deficiencies, excess to then deal with problems that imbalanced chemistry will cause your plant, to correct an imbalance. Nice to know what is in the soil.
Leaf vegey's such as Kale, Lettuce, chard...a little more Nitrogen will not hurt. I still love going with 14-14-14 because it works for both kinds of vegetables; leafy and fruits.
Tell us more information, please because this is a very general answer. If you are growing vegeys inside, we need to discuss light. Daylight length. Size of pot to size of start or seed.
The short answer is Yes, use shop bought compost- and depending on what your growing, use a shop bought vegetable use liquid fertiliser to feed your plants from mid summer onwards- follow the instructions and everything should go ok. In winter get rid of all the compost you used by spreading on your garden- it will be spent and pretty much useless for the next year. Just make sure you use fairly large pots- think no smaller than a beach ball- this will allow room to grow and they wont dry out so fast during the summer. Plants or seed can be bought from a garden center- should come with instructions- don't plant too close and water every night during a dry spell. You might need protection from birds or slugs again ask at the garden center for help- birds you will need netting and canes- not all vegetables will need this, but slugs might be a problem- use the eco friendly version- safe to use round vegies! And buy yourself some good books! build your knowledge up every year- some things will work and others won't- not every garden is the same. Oh and buy some of the strange varieties of vege- don't be boring! and don't grow stuff you can buy for peanuts in the supermarkets- expand your palate! lots of vege come in allsorts of colours and shapes- tomatoes are not just red! nor are carrots just orange either! enjoy yourself, experiment each year with something different.